Extruder

ABSTRACT

An extruder capable of obtaining a treatment volume equal to that of the conventional art without enlarging a screw diameter is provided. The extruder includes screws, a drive unit and a barrel, in which three or more screws having the same diameter and the same root diameter in a waveform shape are engaged with each other and arranged in parallel to each other horizontally or nearly horizontally while a size between axial centers is made equal. According to the above configuration, the same treatment volume as that of the conventional extruder can be handled by screws of the smaller diameter as compared with that of the conventional art. By using the screws of the smaller diameter as compared with the conventional art, temperature irregularities of an extrusion material in screw grooves, leakage of the extrusion material from the screws, an installation area of the extruder, and the like conventional trouble of various kinds can be eliminated.

TECHNICAL FIELD

The present invention relates to an extruder for kneading and extrudinga material through rotation of screws.

BACKGROUND ART

As is shown in FIG. 12, there exists an extruder 10, which extrudes amaterial supplied from a material inlet port 4 to a die part 5 byrotating a screw 1 inserted in a barrel 2 that corresponds to a housingand has a heater thereat by a driving part 3, the extruder 10transferring while heating and kneading the material in the barrel 2(for example, with reference to a cited document 1: publishedspecification of Japanese Patent Laid-Open No. 5-50424). As the extruder10 in this configuration, there are a type having one screw 1 andanother type having two screws 1. The twin-screw type with two screws 1meshed with each other is divided to one in which each screw 1 rotatesin the same direction as shown in FIGS. 13 and 15, and one in which eachscrew rotates in a different direction as shown in FIG. 14. Also withrespect to a shape of the screw 1, there are a trapezoidal screw shapeas indicated in FIGS. 13 and 14, and a waveform screw shape as indicatedin FIG. 15 other than the trapezoidal screw shape.

Furthermore, there are extruders having three or more screws. Theseextruders are constructed in such forms that many screws are arrangedcircumferentially as indicated in FIG. 16, two sets each consisting ofmutually engaged two screws are separately arranged while the screws arenot engaged with each other between the sets, and each screw in the sameset rotates in the same direction while the screws are made to rotate indifferent directions between different sets. Conventionally no extruderis present in which three or more the aforementioned waveform screws arearranged horizontally and meshed with each other to rotate in the samedirection.

For the twin-screw extruder with two screws engaged as above, anincrease of the quantity of the material to be extruded, that is, anincrease of the treatment volume is required. To cope with this, in FIG.17, a diameter D of the screw 1 is increased and moreover, a rootdiameter 17 of the screw 1 is decreased, in other words, a depth 16 ofthread grooves of the screw 1 is made larger regardless of the rotationdirection and the shape of the screw in the conventional art. Here, “toincrease the screw diameter” is taken for the case that the screwdiameter exceeds approximately 90 mm.

However, to increase the screw diameter results in an elongated facilitylength, and also an increase of a mechanical loss and an increase of adriving current of the screw due to a large rotation weight of the screwor the like. Moreover, since the barrel shape is enlarged as well, ittakes time for the heater to raise temperatures. When a large screw isdesigned, normally, a sectional shape of the large screw is madegeometrically similar to a sectional shape of a small screw, and a valueof L/D which is a ratio of a screw outer circumference moving distancewhen the screw rotates once and a groove depth of the screw is madeconstant. Under this condition, a peripheral velocity at the large screwis turned faster as compared with the small screw, whereby aself-heating value because of kneading of the material present in threadgrooves of the screw is increased and the material is degraded.Furthermore, the above speeding up of the peripheral velocitynecessitates considerations to abrasion of the screw and the barrel.

Meanwhile, to increase the groove depth of the screw 1 makes a flightangle 19 of the screw denoted in FIG. 17 smaller. This reduction of theflight angle 19 decreases an abrasion resistance of the screw 1, and atthe same time increases a leak amount of the material from the screw 1.Since a shaft diameter 18 of the screw 1 is reduced when the groovedepth 16 of the screw 1 is increased, it brings about the problem interms of a strength of the screw 1.

Taking the above problem into consideration, to increase the screwdiameter, that is, to increase the groove depth for increasing thetreatment volume is not necessarily a good way. In general, when anextruder with a large diameter screw is to be designed, experiments arecarried out with the use of an experimental extruder with a smalldiameter screw, and a mix proportion of materials to be treated, a screwshape and the like at the actual machine with the large diameter screware determined on the basis of the acquired empirical data. However, itis the reality that the actual machine does not always bear the sameresult as designed because of a difference of the screw diametersbetween the experimental machine and the actual machine, and the like.

The present invention is devised to solve the above-described problem,and has for its object to provide an extruder capable of obtaining atreatment volume equal to that of the conventional art withoutincreasing a screw diameter.

DISCLOSURE OF INVENTION

An extruder of the first aspect of the present invention comprises:

-   -   three or more screws with the same diameter and the same root        diameter in a waveform shape, which are engaged with each other        and arranged in parallel to each other horizontally or nearly        horizontally while a size between axial centers of the screws is        made equal;    -   a drive unit which is configured to rotate all of the screws at        the same velocity in the same direction; and    -   a barrel with a screw fitting part in which all of the screws        are inserted rotatably and which is configured to knead and move        an extrusion material present in a thread groove of the screw to        a thread groove of the adjacent screw through rotation of the        screws by the drive unit.

The extruder may be designed so that the diameter of the screw is 50 mmor smaller.

The extruder may be designed so that the extruder further includes amolding section attached to the barrel for molding the extrusionmaterial extruded by the screws.

An extruder according to the first aspect of the present inventionincludes screws, a drive unit and a barrel. Three or more screws areinstalled, each formed in a waveform shape with the same diameter andthe same root diameter. The screws are engaged with each other while adistance between axial centers of the screws is made equal, and arearranged in parallel to each other horizontally or nearly horizontally.According to the configuration, a treatment volume equal to that of theconventional extruder can be handled by screws with a small diameter ascompared with the conventional one. Using the screws with the smalldiameter as compared with the conventional one can eliminateconventional various kinds of trouble such as a change of a screwperipheral velocity, temperature unevenness of a material for extrusionin screw grooves, leakage of the material for extrusion from screws anda setting area of the extruder.

Further because of attaching the molding section, the extrusion materialextruded by the screws can be molded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of screws installed in an extruder of anembodiment of the present invention;

FIG. 2 is a sectional view of the screws shown in FIG. 1;

FIG. 3 is a side view of the extruder of the embodiment of the presentinvention;

FIG. 4 is a diagram for explaining a state in which a material forextrusion is transferred by the screws shown in FIG. 1;

FIG. 5 is a diagram for explaining a state in which the material forextrusion is transferred by the screws shown in FIG. 1;

FIG. 6 is a diagram for explaining a state in which the material forextrusion is transferred by the screws shown in FIG. 1;

FIG. 7 is a diagram for explaining a route whereby the material forextrusion is transferred in a barrel by the screws shown in FIG. 1;

FIG. 8 is a diagram for explaining an arrangement example of fourscrews;

FIG. 9 is a diagram for explaining an arrangement example of the fourscrews;

FIG. 10 is a diagram for explaining a flight angle at the screw;

FIG. 11 is a diagram showing a structure of a reduction gear installedin a drive unit shown in FIG. 3;

FIG. 12 is a diagram showing a constitution of a conventional extruder;

FIG. 13 is a diagram indicative of a form example of screws installed inthe extruder shown in FIG. 12;

FIG. 14 is a diagram indicative of a form example of screws installed inthe extruder shown in FIG. 12;

FIG. 15 is a diagram indicative of a form example of screws installed inthe extruder shown in FIG. 12;

FIG. 16 is a sectional view of a conventional extruder with multiplescrews;

FIG. 17 is a diagram for explaining each part in a conventionaltwin-screw; and

FIG. 18 is a diagram showing a structure of a cutting device connectibleto the extruder shown in FIG. 3.

BEST MODE FOR CARRYING OUT THE INVENTION

An extruder as an embodiment of the present invention will be describedbelow with reference to the drawings. It is to be noted that like partsare designated by like reference numerals through the drawings.

As shown in FIG. 3, an extruder 100 of the embodiment includes screws101, a barrel 102 and a drive unit 103, and can further be equipped witha die 105 which corresponds to a molding section. In the presentembodiment, the barrel 102 has a material supply part 104 for a material131 for extrusion, a vent part 108 as an air vent part for the material131 transferred by the screws 101, and a heating/cooling device 107 forheating or cooling the material 131. FIG. 1 shows a form in which ahopper 106 for storing the material 131 is attached to the materialsupply part 104. However, the extruder 100 is not limited to this formand can be of a form with another extruder connected thereto forforcibly or quantitatively supplying the material 131 to the materialsupply part 104. An example of the material 131 for extrusion is amixture in a solid state of plastic and a filler. The solid state is,for instance, a state of pellets or powder.

According to the embodiment and as indicated in FIGS. 1 and 2, thescrews 101 comprises four screws 101-1 to 101-4 each of a waveform shapewith the same diameter 111, the same root diameter 112, and the sameratio of the diameter 111 and the root diameter 112. The screws 101-1 to101-4 are engaged with each other and arranged in parallel to each otherhorizontally or nearly horizontally while a size 113 between mutualaxial centers is made equal. The aforementioned “nearly horizontally”means a positional deviation of each of the screws 101-1 to 101-4 within±θ degrees with respect to a horizontal axis centering a central part ina horizontal direction of the four screws 101-1 to 101-4. Specifically,the above θ is 5 degrees, preferably 3 degrees.

Although four screws 101 are arranged in the present embodiment asdescribed hereinabove, the present invention is not limited to this, andthree or more screws can be installed.

Since it is preferable that no change is generated in the screw diameterbetween the experimental machine and the actual machine as discussedearlier, and also from a viewpoint of making a depth 118 of a screwgroove 114 shallow as will be described later, the diameter 111 of eachof the screws 101 is preferably not larger than 50 mm. From thisviewpoint, each screw 101 having the diameter 111 of, e.g.,approximately 12-15 mm can be used. In an exceptional case, three ormore screws 101 having the diameter 111 of, for instance, approximately150 mm are arranged.

The barrel 102 has an inner face 121 which forms a screw fitting part120. The screw fitting part 120 has a shape so that all of the screws101-1 to 101-4 can be fitted rotatably under the above-describedarrangement condition, specifically, a shape with a plurality of gourdscoupled along the horizontal direction.

In the case of designing a barrel for storing four screws on the basisof a conventionally existing barrel for storing two screws, two methodscan be considered, namely, a method of arranging two sets each havingtwo screws 201, with a clearance 202 formed between the sets as shown inFIG. 8, and a method of arranging one screw set 205 and the other screwset 207 so that a barrel inner face 206 for storing the one screw set205 and a barrel inner face 208 for storing the other screw set 207contact with each other in a tangent direction as shown in FIG. 9. Inthe case shown in FIG. 8, however, the clearance 202 marked by obliquelines and its adjoining region should be heated and cooled more than theother parts in the barrel because of the need of heating or cooling thematerial 131 at each of the screw sets 205 and 207, thereby causing thebarrel to be large. On the other hand, in the case shown in FIG. 9, edgeportions 209 and 210 of the barrel present at contact parts between theinner face 206 and the inner face 208 should be removed to prevent theedge portions 209 and 210 from being broken. As a result, the removedportions become dead spots to collect the material, leading to a problemof thermal degradation of the material, or the like.

As such, according to the present embodiment as shown in FIG. 2, thescrews 101-1 to 101-4 are arranged so that a clearance 115 between aroot of the screw 101-1 and a crest of the screw 101-2, a clearance 116between a root of the screw 101-3 and a crest of the screw 101-4, and aclearance 117 between a crest of the screw 101-2 and a root of the screw101-3 become all equal to each other.

The screw fitting part 120 as above kneads the material 131 present inthe thread groove 114 of each of the screws 101-1 to 101-4 through therotation of the screws 101 by the drive unit 103 in a direction of anarrow 135 as indicated in FIGS. 4-7. In other words, the material 131present in each thread groove 114 is rotated and kneaded within thethread groove 114 as designated by an arrow 134 through the rotation ofthe screws 101. Each material 131 while being kneaded is moved to thethread groove 114 of the adjoining screws 101 in a direction of an arrow132 indicated in FIG. 1. In the whole of the screw fitting part 120 inthe barrel 102, the material 131 is moved while being kneaded in asequence from the screw 101-1 to the screw 101-2 to the screw 101-3 tothe screw 101-4 to the screw 101-3 to the screw 101-2 to the screw 101-1along the shape of the inner face 121 as indicated by an arrow 133 inFIG. 7.

By including the barrel 102 having the screw arrangement and the innerface 121 as shown in FIG. 2, a filling situation and a kneading state ofthe material 131 can be made equal at each of the screws 101-1 to 101-4.

Supposed that an extrusion amount of the material 131 is kept the sameas in the conventional case having a large diameter and two screws, if asection in a diametrical direction of the screw is made geometricallysimilar to that of the twin-screw and the number of screw is made threeor more, the diameter of the screw can be made small as compared withthe conventional art and the depth 118 of the thread groove 114 of thescrew can be made shallow. Accordingly, a surface length and a barrelinner face length of the screws 101 become long as compared with theconventional art. The number of position change times of the material131 is increased because of the above increase of the surface length andthe inner face length in comparison with the conventional art, so that akneadability of the material 131 can be improved in comparison with thecase of the conventional twin-screw extruder having the large diameterof the screw.

Further, since the depth 118 of the thread groove 114 is renderedshallow owing to the reduction of the screw diameter 111, temperatureirregularities at the material 131 present in one thread groove 114 arereduced. Particularly when the material has a large self-heating value,the self-heating value can be decreased because the screw diameter 111can be reduced. According to the extruder 100 of the embodiment, theextrusion amount of the material 131 can be controlled by the number ofthe screws 101 in a state while a change of physical properties of thematerial 131 is lessened more.

The above reduction of the screw diameter saves energy and can reducemechanical loss, which is suitable for small production in a variety ofkinds and improves the operability.

Since also the barrel 102 is made compact by the reduction of the screwdiameter 111, heat conduction of heating and cooling to the barrel 102can be improved.

In addition, since the thread grooves 114 of the screws 101 communicatewith the material supply part 104 and the vent part 108, and the depth118 of the thread groove 114 is shallow as described above, air ventfrom the material 131 is facilitated.

The reduction of the screw diameter 111 increases the flight angle 119of each screw 101. More specifically, the flight angle can beapproximately 20 degrees or larger. Therefore, in comparison with a casewhere the screw diameter is increased, the abrasion resistance betweenscrews 101 can be improved while the same treatment volume is secured,and at the same time, a leak amount of the material 131 from the screws101 can be reduced. A lead of each of the screws 101 is shortened by thereduction of the screw diameter 111 and the increase of the flight angle119, and consequently the extrusion amount of the material 131 isreduced. However, the reduced amount can be compensated by increasingthe number of screws 101.

According to the extruder 100 of the present embodiment as above, thediameter 111 of each screw 101 can be reduced by controlling theextrusion amount of the material 131 by the number of the screws 101,and this reduction can solve conventional various kinds of trouble suchas the change of the screw peripheral velocity, temperatureirregularities of the material 131 in the screw groove 114, leakage ofthe material 131 from the screws 101, an installation area of theextruder 100 and the like. Moreover, since the number of the screws 101can be increased in conformity with a target extrusion amount, the screwgroove 114 can be made shallow by the increase of the screw as above,and the temperature irregularities of the material 131 can be improved,thus enabling molding of the material improved in heating/coolingefficiency. The larger the screw number is made, the more portions thescrews are engaged with each other at. Therefore, the heating/coolingefficiency can be enhanced as above while the self-cleanability of thescrews 101 is maintained.

In the above embodiment, the shape of each of screws 101 is exemplifiedby a two-thread screw. The same effect as above can be obtained by asingle-thread screw or three-thread screw. The shape of each of thescrews 101 is changeable from viewpoints of the abrasion of the screwand the leakage of the material 131 from an outer circumferential partof each of the screws 101.

The foregoing description is based on the assumption that the material131 never leaks from a gap between the screws 101 and the barrel 102except the case related to leakage of the material 131 because of thechange of the flight angle 119.

The drive unit 103 will be described. The drive unit 103 is equippedwith, as shown in FIG. 1, a motor 141 as a driving source for rotatingthe screws 101, and a reduction gear 142 with the motor 141 connectedthereto which decelerates and transmits the rotation of the motor 141 tothe screws 101. As shown in FIG. 11, the reduction gear 142 has oneinput gear 143 connected to the motor 141, four screw drive gears 144connected to the screws 101-1 to 101-4 respectively, and two idle gears145 which couple the above input gear 143 and the screw drive gears 144with each other. A stage number and a reduction gear ratio of gears fordriving the screw 101 are equal for each of the screws 101-1 to 101-4 inthe reduction gear 142. The stage number and the reduction gear ratio ofgears for driving each screw are adjusted so as to become equal to eachother by the idle gears even when the number of the screw exceeds four.

The stage number of gears for driving each of the screws 101-1 to 101-4becomes two by using the reduction gear 142 of the above configuration,so that a difference of cumulated backlash of gears can be reduced. Aclearance between flights of the screws 101 can be narrowed, andaccordingly the leak of the material 131 from the screws 101 can bereduced.

A comparison between an example of the extruder 100 of the presentembodiment with the above-described configuration, and the conventionalextruder will be discussed below.

In the conventional twin-screw extruder, the treatment volume of 50kg/hour of the material 131 which includes PP (polypropylene), rubberand talc is obtained at a molding temperature of 210 degrees and byrotating the screw by 400 rpm while the screw diameter is 40 mm and theL/D is 30. In a case where the same treatment volume is to be handled bythe extruder 100 of the embodiment, the extruder comes to be equippedwith four screws 101 of the diameter of 30 mm, and the L/D is made 30.Since the screws 101 are made geometrically equal to the conventionalone of the screw diameter of 40 mm, therefore a total length of thescrew 101 is shortened from 1200 mm to 900 mm. In other words, a totallength of the extruder 100 can be reduced by 33%, and a screw weight canbe reduced by approximately 18%, an installation area can be reduced,heat energy by the heater or the like can be reduced because of areduction of a heating/cooling zone.

A working device for working objects molded by the die 105 can beconnected to a discharge side of the die 105. When the material 131 ismolded by the die 105 into, e.g., a cylindrical shape, an example of theworking device includes a water bath for cooling the object molded bythe die 105, and a cutting device 160 shown in FIG. 18 for cutting themolded object which passes the water bath to a constant length. Theproduct cut by the cutting device 160 becomes, for example, a pelletshape of a diameter of approximately 3 mm and a length of approximately3 mm.

The cutting device 160 has rollers 162 for further shaping the shape ofthe molded object 161 cooled in the water bath, a fixed blade 163 and arotary blade 164. The molded object 161 supplied continuously from therollers 162 onto the fixed blade 163 is cut by the rotary blade 164which is rotating in a direction of an arrow 165, to be the product 166.

In the above description, the extruder 100 of the embodiment isdescribed to be able to obtain the same treatment volume as that of theconventional twin-screw extruder with the large diameter. When thetreatment volume is compared between the extruder 100 of the presentembodiment having four screws 101 of the same diameter as the screwdiameter of the conventional twin-screw extruder, and the conventionaltwin-screw extruder, although the treatment volume is apparentlyconsidered to be double since the number of screws is twice as many, theextruder 100 of the present embodiment can actually achieveapproximately 2.5 to 3 times a throughput of the conventional extruder.The reason for this is considered as follows. As shown in FIGS. 4-7, thematerial 131 moves in each groove 114 in the direction denoted by thearrow 133. At this time, surfaces of adjacent screws 101 shift inopposite directions as indicated by arrows at portions where grooves 114formed by adjacent screws 101 intersect, for instance, at V-shapedportions marked by a reference numeral 137 in FIG. 5. In consequence,moving direction of the material 131 is switched in the V-shape as ismade clear by the arrows, and a shear rate is further increased. Ameltability and a kneadability of the material 131 are improved byeffects produced by the switching of the moving direction. That is, themeltability and the kneadability can be improved by increasing thenumber of the V-shaped portions 137. There are six V-shaped portions 137present in the extruder 100 of the embodiment, whereas there are twoV-shaped portions in the conventional twin-screw extruder.

Additionally, as shown in FIG. 2, in each screw 101, two clearancesbetween the crests and the inner face 121 of the barrel 102, and theclearance 115 to the adjacent screws 101, i.e., a total of threeclearances are designed considerably narrow in comparison with theconventional machine. Hence the screws 101 are engaged tightly with eachother, and an effect of scraping the material 131, so-called wipingeffect at surfaces of the engaged counterpart screws 101 is enhancedgreatly. Thus since leakage of the material 131 from each part isreduced, the throughput is increased.

Because of the above-described switching effect and the wiping effect,it can be said that the extruder 100 of the present embodiment canachieve approximately 2.5 to 3 times the throughput of the conventionalextruder.

Any suitable combination of the above various embodiments can exertrespective effects.

Although the present invention has been fully described in connectionwith the preferred embodiment thereof with reference to the accompanyingdrawings, it is to be noted that various changes and modifications areapparent to those skilled in the art. Such changes and modifications areto be understood as included within the scope of the present inventionas defined by the appended claims unless they depart therefrom.

1-4. (Canceled)
 5. An extruder, which comprises: three or more screwswith the same diameter and the same root diameter in a waveform shape,which are engaged with each other and arranged in parallel to each otherhorizontally or nearly horizontally while a size between axial centersof the screws is made equal; a drive unit which is configured to rotateall of the screws at the same velocity in the same direction; and abarrel with a screw fitting part in which all of the screws are insertedrotatably and which is configured to knead and move an extrusionmaterial present in a thread groove of the screw to a thread groove ofthe adjacent screw through rotation of the screws by the drive unit, allof the screws inserted in the screw fitting part being disposed so as toengage tightly with each other while clearances each between the threadgroove of one of the engaged screws and a crest of the other of theengaged screws are made constant, and at the same time, the clearancesand a clearance between the crest of the screw and an inner face of thebarrel are made so narrow as to reduce leakage of the extrusion materialfor whole of the adjoining screws, the extrusion material being movedtransferring the thread grooves of all of the screws along the innerface of the barrel by the rotation of the screws in the same direction.6. The extruder according to claim 5, wherein the diameter of each ofthe screws is 50 mm or smaller.
 7. The extruder according to claim 5,which further comprises a molding section installed to the barrel andconfigured to mold the extrusion material extruded by the screws.
 8. Theextruder according to claim 6, which further comprises a molding sectioninstalled to the barrel and configured to mold the extrusion materialextruded by the screws.
 9. The extruder according to claim 5, whereinthe screw fitting part has switching portions configured to switch amoving direction of the extrusion material so as to improve kneadabilityof the extrusion material when the extrusion material present in thethread groove of the screw is moved to a thread groove of the adjacentscrew, the extrusion material being moved transferring all of theswitching portions formed in the screw fitting part along the inner faceof the barrel by the rotation of the screws in the same direction. 10.The extruder according to claim 5, wherein the screws are arranged witha shift of every 90 degrees between a crest of one screw and a crest ofthe adjacent other screw when the screws are formed by a two-threadscrew.